DNA is cleaved by the 2:1 1,10-phenanthroline-cuprous complex in a reaction which requires hydrogen peroxide. The reaction proceeds through an intercalative intermediate involving the DNA and the coordination complex and yields products which are effective inhibitors of E. coli Po1 I and other polymerases. The strand scission appears to result from the degradation of a deoxyribose moiety. The structures of the products of the reaction, in particular the fate of deoxyribose, are under investigation. The function of tightly bound zinc ion in RNA and DNA polymerases is being studied with (a) spectroscopic probes of the tightly bound zinc ion; (b) the kinetics of removal of zinc ion by chelating agents; and (c) the kinetics of exchange of zinc-65 into the protein. The perturbation of substrates on the reactivity of the zinc will be used to deduce the role of the metal ion.